Enzyme Properties and Catalysis

Overview of Enzymes

• Enzymes catalyze reactions that are essential for life, acting differently from chemical catalysts.

• They facilitate biochemical reactions, allowing for the rapid conversion of substrates into products under mild conditions.

Five Properties of Enzymes

1. Speed of Reaction

   • Enzymes accelerate the rate of biochemical reactions, sometimes by up to 10^12 times compared to uncatalyzed reactions.

   • They ensure that biological reactions occur quickly enough to sustain life.

2. Lower Activation Energy

   • Enzymes lower the activation energy required for reactions, enabling them to proceed at lower temperatures and pressures typical for cellular environments.

3. Specificity

   • Enzymes are highly specific; each type of enzyme catalyzes a particular reaction or set of reactions, minimizing unwanted side reactions.

4. Regulation

   • Enzymes can be turned on or off, making them adaptable to the needs of the cell. Cells can regulate the metabolism by controlling enzyme activity.

5. Coupling Reactions

   • Enzymes can couple spontaneous reactions (which happen naturally) to non-spontaneous reactions (which require energy input), facilitating vital processes.

Cofactors

• Definition: Cofactors are non-protein substances that assist enzymes in catalyzing reactions.

  • Types of Cofactors:

    • Inorganic (e.g., metal ions like magnesium, copper, zinc, iron)

    • Organic (called coenzymes, e.g., NAD, coenzyme A, heme, FAD)

• Importance of Cofactors:

  • Essential for the catalytic activity and structural stability of enzymes.

  • They can play roles in electron transfer during oxidation-reduction reactions, which are vital for energy metabolism.

Enzyme Mechanisms

• Enzymes facilitate reactions by binding substrates and orienting them correctly for reaction, which reduces the energy barrier.

• Curved Arrows: Indicate the movement of electrons or electron pairs in reaction mechanisms, not the movement of nuclei.

Examples of Enzyme-Catalyzed Reactions

• Alcohol Dehydrogenase: Catalyzes the oxidation of ethanol to acetaldehyde using NAD+ as a coenzyme, illustrating the concept of coenzyme regeneration.

Historical Context

• Initial discoveries about enzymes originated in the 1800s, notably through studies on fermentation by French chemists like Pasteur, who investigated yeast's ability to convert glucose into ethanol.

Distinction of Enzymes from Other Catalysts

• While both enzymes and chemical catalysts increase reaction rates, enzymes operate under physiological conditions, maintain specificities, and are subject to cellular regulation.